Method of manufacturing magnetic particles, magnetic particles, and magnetic recording medium

Abstract

A method of manufacturing magnetic particles, the method comprising synthesizing iron particles in a liquid phase, nitriding the iron particles, adjusting the average particle diameter to 5 to 25 nm, and making the iron particles substantially spherical. Also provided are magnetic particles and magnetic recording media.

1 . A method of manufacturing magnetic particles, the method comprising synthesizing iron particles in a liquid phase, nitriding the iron particles, adjusting the average particle diameter to 5 to 25 nm, and making the iron particles substantially spherical.  
     
     
         2 . The method of manufacturing magnetic particles described in  claim 1 , wherein the synthesis of the iron particles comprises conducting a reduction reaction by mixing a reverse micelle solution (II) and a reverse micelle solution (I), wherein the reverse micelle solution (II) is prepared by mixing a water-insoluble organic solvent containing a surfactant and an aqueous solution of a reducing agent, and the reverse micelle solution (I) is prepared by mixing a water-insoluble organic solvent containing a surfactant and an aqueous solution of a salt of iron.  
     
     
         3 . The method of manufacturing magnetic particles described in  claim 1 , further comprising forming an oxide layer.  
     
     
         4 . The method of manufacturing magnetic particles described in  claim 2 , wherein the surfactant is an oil-soluble surfactant.  
     
     
         5 . The method of manufacturing magnetic particles described in  claim 2 , wherein the aqueous solution of the salt of iron contains a chelating agent.  
     
     
         6 . The method of manufacturing magnetic particles described in  claim 2 , wherein each of the reverse micelle solutions (I) and (II) has a water/surfactant ratio in a range of 0.5 to 20.  
     
     
         7 . The method of manufacturing magnetic particles described in  claim 2 , wherein the reduction reaction is conducted at a constant temperature in a range of −5° C. to 30° C.  
     
     
         8 . The method of manufacturing magnetic particles described in  claim 2 , wherein the reduction reaction is conducted while stirring at a rate of 3,000 rpm or higher.  
     
     
         9 . The method of manufacturing magnetic particles described in  claim 2 , wherein after the reduction reaction, at least one dispersant having one to three groups selected from amino groups and carboxyl groups is added in an amount of 0.001 to 10 moles per mole of the iron particles to be produced.  
     
     
         10 . The method of manufacturing magnetic particles described in  claim 9 , wherein the dispersant has 1 to 3 groups selected from amino, carboxyl, sulfonate and sulfinate groups.  
     
     
         11 . The method of manufacturing magnetic particles described in  claim 2 , wherein after the reduction reaction, the iron particles are ripened for 5 to 180 minutes at a constant temperature in a range of 30° C. to 90° C.  
     
     
         12 . The method of manufacturing magnetic particles described in  claim 2 , wherein the iron particles are reduced in hydrogen or a mixed gas stream of hydrogen and an inert gas prior to nitriding.  
     
     
         13 . Magnetic particles containing at least a Fe 16 N 2  phase having an average particle diameter of 9 to 11 nm and a particle diameter variation coefficient of 15% or less.  
     
     
         14 . The magnetic particles described in  claim 13 , wherein the magnetic particles are free from any phase of iron nitride other than the phase of Fe 16 N 2 .  
     
     
         15 . The magnetic particles described in  claim 13 , wherein the content of nitrogen is 1.0 to 20.0 atom % relative to iron.  
     
     
         16 . The magnetic particles described in  claim 13 , wherein the content of nitrogen is 8.0 to 15.0 atom % relative to iron.  
     
     
         17 . The magnetic particles described in  claim 13 , wherein surfaces of the magnetic particles have an oxide layer having a thickness of 1 to 5 nm.  
     
     
         18 . The magnetic particles according to  claim 13 , wherein the Fe 16 N 2  phase has a coercive force of 197.5 to 237 kA/m (2,500 to 3,000 Oe) and a Ms·V value of 5.2×10 −16  to 6.5×10 −16 .  
     
     
         19 . A magnetic recording medium containing magnetic particles described in  claim 13  in a magnetic layer.  
     
     
         20 . A magnetic recording medium containing magnetic particles described in  claim 18  in a magnetic layer.